The production of nitrites by ammoxidation of an appropriate alkene in the presence of a suitable catalyst is well known. The production of acrylonitrile from a gaseous feed of propylene, ammonia and air is described by Bruce E. Gates et al., in Chemistry of Catalytic Processes, McGraw-Hill (1979), pp.380-384.
The feed is sent to an ammoxidation reactor where, in the presence of a suitable catalyst, acrylonitrile is produced along with lesser amounts of other nitrogen-containing compounds. The effluent from the ammoxidation reaction is first quenched and then contacted countercurrently with water in an absorption tower. The desired products are recovered from the absorber in the aqueous phase. The absorbed off gas, typically oxygen, carbon dioxide, carbon monoxide, nitrogen and unreacted hydrocarbon are combined with natural gas and sent to a boiler for combustion. See, U.S. Pat. Nos. 3,591,620 and 4,335,056.
The unreacted feed material may be recovered. For example, U.S. Pat. Nos. 4,849,537, 4,870,201 and 5,015,756 teach the use of pressure swing adsorption type separators to recover unreacted propylene in an acrylonitrile process. The use of oxygen enriched air is generally coupled with a pressure swing adsorption separator.
U.S. Pat. No. 5,466,857 relates to reducing the amount of unreacted ammonia during the ammoxidation process by adding an additional amount of oxygen to the lower portion of a fluidized bed so that the oxygen can react with the unreacted ammonia. U.S. Pat. No. 5,457,223 relates to reducing ammonia breakthrough during the ammoxidation process by adding an additional amount of oxygen to the upper portion of a fluidized bed to react with unreacted ammonia.
Japanese Application No. 551980!-83,452 relates to a single source of oxygen which is split into two streams in which one of the streams is premixed with ammonia and the hydrocarbon reactant.
The art does not address or remedy the undesirable but important aspect of the presence of inerts in the ammoxidation process. "Inerts" in the general sense is defined herein as chemical species that are substantially non-reactive at the conditions at which the ammoxidation take place. In air based ammoxidation, the primary inert is nitrogen. As the presence of inerts in the ammoxidation process corresponds to a decrease in acrylonitrile yield, removing or decreasing the inerts is believed to increase the yield of the final acrylonitrile yield of the ammoxidation reaction therefrom.